Nucleic acid vaccine against the sars-cov-2 coronavirus

ABSTRACT

The invention relates to an immunogenic or vaccine composition against the 2019 novel coronavirus (SARS-CoV-2), comprising a nucleic acid construct encoding a SARS-CoV-2 coronavirus Spike (S) protein antigen or a fragment thereof comprising the receptor-binding domain, wherein the nucleic acid construct sequence is codon-optimized for expression in human.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation U.S. application Ser. No. 17/819,187 filed on Aug. 11, 2022, which is a continuation of International Appln. PCT/EP2021/025053, filed on Feb. 12, 2021, which itself claims the benefit of U.S. provisional application 62/976,148 filed on Feb. 13, 2020, and European Appln. EP 20305140.4 filed on Feb. 13, 2020, the contents of each of which are incorporated herein by reference in their entireties for all purposes.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

The instant application contains a Sequence Listing which has been submitted electronically in XML format and is hereby incorporated by reference in its entirety. Said XML copy, created on Jul. 12, 2023, is named B2006132EPWOUS.xml and is 191,004 bytes in size.

FIELD OF THE INVENTION

The invention relates to an immunogenic or vaccine composition against the 2019 novel coronavirus (SARS-CoV-2, 2019-nCov or COVID-19), comprising a nucleic acid construct encoding a SARS-CoV-2 coronavirus Spike (S) protein antigen or a fragment thereof comprising the receptor-binding domain (RBD), wherein the nucleic acid construct sequence is codon-optimized for expression in human. The invention also relates to said nucleic acid construct, derived vector, antigen encoded by said nucleic acid construct and to their use for the diagnosis, prevention and treatment of SARS-CoV-2 coronavirus infection.

BACKGROUND OF THE INVENTION

In December 2019, patients presenting with viral pneumonia were reported in Wuhan, China. A novel coronavirus was subsequently identified as the causative agent, and provisionally named 2019 novel coronavirus (2019-nCov or SARS-CoV-2) (Zhu N et al., N Engl J Med., 2020 Jan. 24). The virus swiftly spread within and outside China, leading to the WHO declaring a Public Health Emergency of International Concern on Jan. 30, 2020. With the aim of rapid development of a candidate vaccine, and based on the state of the art of betacoronaviruses biology, two suitable candidate antigens based on the spike (S) protein of the virus were designed.

Coronaviruses are enveloped, positive single stranded RNA viruses. Coronaviruses have been identified in various mammalians hosts such as bats, camels, or mice, among others. Several coronaviruses are pathogenic to human, leading to varying degrees of symptoms severity (Cui et al., Nat Rev Microbiol. 2019 March; 17(3):181-92). Highly pathogenic variants include the severe acute respiratory syndrome coronavirus (SARS-Cov) that emerged in China in 2002, resulting in ˜8000 human infections and 700+ deaths (Peiris et al., Nat Med., 2004 December; 10(12 Suppl):S88-97) and the Middle East respiratory syndrome coronavirus (MERS-CoV), first detected in Saudi Arabia in 2012 and responsible for ˜2500 human infections and 850+ deaths (Zaki et al., N Engl J Med., 2012 Nov. 8; 367(19):1814-20; Lee et al., BMC Infect Dis. 2017 Jul. 14; 17(1):498).

Coronaviruses genomes encode non-structural polyprotein and structural proteins, including the Spike (S), envelope, membrane and nucleocapsid proteins. As seen notably with SARS-Cov, neutralizing antibodies and/or T-cell immune responses can be raised against several proteins but mostly target the S protein, suggesting that S protein-induced specific immune responses play important parts in the natural response to coronavirus infection (Saif L J, Vet Microbiol. 1993 November; 37(3-4):285-97). The S glycoprotein has key roles in the viral cycle, as it is involved in receptor recognition, virus attachment and entry, and is thus a crucial determinant of host tropism and transmission capacity. Expressed as precursor glycoprotein, S is cleaved in two subunits (S1, which contains the receptor binding domain (RBD), and S2) by proteases.

There is a need for new vaccines to control SARS-CoV-2 virus infection.

SUMMARY OF THE INVENTION

The inventors have engineered a nucleic acid vaccine against the 2019 novel coronavirus (SARS-CoV-2 or 2019-nCov) based on its Spike (S) protein coding sequence available in sequence data bases, which has been optimized for expression in human. Various nucleic acid constructs containing either the complete SARS-CoV-2 Spike, a Spike modified at the furin site), stabilized with proline residues and/or comprising a C-terminal deletion, or only the receptor binding domain (RBD) were engineered using the optimized Spike coding sequence. To ensure that the antigen will be able to generate a broad immune response that will also result in protection against novel variants of SARS-CoV-2, inventors included point modifications of the antigen in key areas of the spike and its RBD. This notably involved modifications close to the pocket of contact with the receptor ACE2 (region 480-505), as well as regions along the spike where changes (mutations or deletion) have been noted during the natural circulation of the virus in human. Animals were vaccinated with formulation of the various nucleic acid constructs by intramuscular, intranasal, or mixed administration using various prime boost immunization regimens. Nucleic acid vaccine was able to induce neutralizing antibody production. In correlation with strong neutralizing antibody induction, nucleic acid vaccine encoding the RBD antigen was able to provide protection from a SARS-CoV-2 challenge of immunized animals, The various derivatives of the initial antigen will be used in a composition or sequentially in prime boost regimens.

Therefore, the invention relates to an immunogenic or vaccine composition against SARS-CoV-2 virus comprising a nucleic acid construct encoding a SARS-CoV-2 virus Spike (S) protein antigen having at least 90% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2 or a fragment thereof comprising the receptor-binding-domain (RBD), wherein the nucleic acid construct sequence is codon-optimized for expression in human.

In some embodiments of the composition according to the invention, the nucleic acid construct comprises a sequence chosen from SEQ ID NO: 1, SEQ ID NO: 3, and the nucleotide sequences having at least 80% identity with said sequences.

In some preferred embodiments of the composition according to the invention, said nucleic acid construct comprises a Kozak sequence.

In some preferred embodiments, the nucleic acid construct comprises a sequence selected from the group consisting of SEQ ID NO: 10, 12, 14, 16, 18, 20, 22, 24, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, the nucleotide sequences having at least 80% identity with said sequences, and the RNA sequences thereof; preferably selected from the group consisting of SEQ ID NO: 14, 16, 18, 20, 22, 24, 31, 33, 35, 37, the nucleotide sequences having at least 80% identity with said sequences, and the RNA sequences thereof.

In some embodiments of the composition according to the invention, said RBD fragment comprises an amino acid sequence having at least 90% identity with SEQ ID NO: 4.

In some preferred embodiments of the composition according to the invention, said S protein antigen or RBD fragment thereof comprises a signal peptide, preferably selected from the group consisting of the sequences SEQ ID NO: 5, 6 and 7.

In some preferred embodiments of the composition according to the invention, said S protein antigen or RBD fragment thereof further comprises at least an epitope recognized by human T cells; preferably human CD4+ T-cells; more preferably a Universal Pan HLA-DR Epitope such as PADRE (SEQ ID NO: 8); preferably wherein the S protein antigen or RBD fragment thereof and the epitope are separated by a linker, preferably comprising SEQ ID NO: 9.

In some preferred embodiments of the composition according to the invention, said S protein antigen or RBD fragment thereof comprises an amino acid sequence selected from the group consisting of SEQ ID NO: 11, 13, 15, 17, 19, 21, 23, 25, 30, 32, 34; 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66 and the sequences having at least 90% identity with said sequences; preferably selected from the group consisting of SEQ ID NO: 15, 17, 19, 21, 23, 25, 32, 34, 36, 38, and the sequences having at least 90% identity with said sequences.

In some embodiments of the composition according to the invention, said nucleic acid construct is a mammalian expression cassette, preferably human expression cassette, wherein the coding sequence of said S protein antigen or RBD fragment thereof is operably linked to appropriate regulatory sequence(s) for their expression in an individual's target cells or tissue(s); preferably comprising a promoter; more preferably further comprising one or more of an enhancer, terminator or intron.

In some embodiments of the composition according to the invention, said nucleic construct is RNA or DNA. In some particular embodiments, the RNA is non-replicating or self-amplifying mRNA comprising a cap structure, 5′- and 3′-untranslated regions (UTRs), and a 3′poly(A) tail operably linked to the coding sequence of said S protein antigen or RBD fragment thereof.

In some embodiments, the composition according to the invention comprises a vector comprising said nucleic acid construct; preferably a viral vector, a plasmid, a nucleic acid delivery agent or combination thereof. In some particular embodiments, said nucleic acid construct, preferably an expression cassette, is inserted into a viral vector or a plasmid. The viral vector is advantageously selected from the group consisting of: cytomegalovirus, adenovirus, vesicular stomatitis virus, modified vaccinia virus ankara and measles virus. In some particular embodiments, the nucleic acid delivery agent comprises tetrafunctional non-ionic amphiphilic block copolymers comprising at least one hydrophilic block and at least one hydrophobic block. In some particular embodiments, the plasmid is combined with a nucleic acid delivery agent, preferably comprising tetrafunctional non-ionic amphiphilic block copolymers comprising at least one hydrophilic block and at least one hydrophobic block. In some particular embodiments, the nucleic acid delivery agent comprises a particle or vesicle, in particular lipid-based micro- or nano-vesicle or particle such as liposome or lipid nanoparticle (LNP). In some particular embodiments, the nucleic acid construct is RNA, in particular mRNA according to the present disclosure and the vector is a particle or vesicle, in particular LNP.

In some embodiments of the invention, the immunogenic or vaccine composition further comprises a pharmaceutically acceptable vehicle and/or an adjuvant.

In some embodiments of the invention, the immunogenic or vaccine composition induces humoral and cellular immune responses against said SARS-CoV-2 virus; preferably wherein the humoral immune response comprises neutralizing antibodies against said SARS-CoV-2 virus and/or the cellular immune response comprises CD4+ and/or CD8+ T-cells against said SARS-CoV-2 virus.

The invention also relates to the immunogenic or vaccine composition according to the present disclosure, for use in the prevention or treatment of SARS-CoV-2 virus infection.

The invention also relates to the nucleic construct according to the present disclosure, the vector comprising said nucleic acid construct, the SARS-CoV-2 virus S protein antigen or fragment thereof comprising the receptor binding domain encoded by said nucleic acid construct and to their use for the diagnosis, prevention and treatment of SARS-CoV-2 coronavirus infection.

DETAILED DESCRIPTION OF THE INVENTION Nucleic Acid Construct and Vector

The invention relates to a nucleic acid construct encoding a SARS-CoV-2 virus Spike (S) protein antigen having at least 90% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2 or a fragment thereof comprising the receptor-binding-domain, wherein the nucleic acid construct sequence is codon-optimized for expression in human.

The nucleic acid construct may consist of recombinant, synthetic or semi-synthetic nucleic acid which is expressible in the individual's target cells or tissue. The nucleic acid may be DNA, RNA, mixed and may further be modified. In some embodiments, the nucleic acid construct consists of recombinant or synthetic DNA or RNA, in particular mRNA. The nucleic construct has usually a length of up to 10000 nt. Preferably up to 9000, 8000, 7000, 6000 or 5000 nt.

As used herein “individual” or “subject” refers to a human.

The terms “a”, “an”, and “the” include plural referents, unless the context clearly indicates otherwise. As such, the term “a” (or “an”), “one or more” or “at least one” can be used interchangeably herein.

As used herein, SARS-CoV-2 refers to any isolate, strain or variant of SARS-CoV-2.

As used herein, SARS-CoV-2 infection refers to SARS-CoV-2 infection and associated disease (Covid-19).

The nucleic acid sequences disclosed herein are provided in their DNA form. However, the present invention encompasses the RNA equivalent of any of the disclosed DNA sequences.

SEQ ID NO: 2 is the amino acid sequence of the Spike (S) protein of the 2019 novel coronavirus initially named 2019-nCov and renamed SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2). The S protein comprises a signal peptide (SP) from position 1 to 18 which is cleaved in the mature S protein. The S protein is cleaved into two subunits, S1 which contains the receptor binding domain (RBD) and S2, by proteases. S1 is from positions 19 to 661 of SEQ ID NO: 2 and S2 is from positions 662 to 1270 of SEQ ID NO: 2 (See FIG. 3 ). The receptor binding domain (RBD) is from positions 331 to 524 in SEQ ID NO: 2 and corresponds to SEQ ID NO: 4 in wild-type SARS-CoV-2. By simple sequence alignment with SEQ ID NO: 2, one skilled in the art can easily determine the positions of the RBD in the sequence of a S protein antigen variant or fragment thereof according to the present disclosure. The RBD from wild-type SARS-CoV-2 S protein or S protein antigen variant or fragment thereof according to the present disclosure is highly reactive to anti-S neutralizing antibodies and competitively inhibits SARS-CoV-2 virus neutralisation by said anti-S neutralizing antibodies. Therefore, the S antigen and the S antigen fragment according to the invention which comprises the RBD (RBD fragment, RBD antigen or RBD antigen fragment) are highly reactive to anti-S neutralizing antibodies and competitively inhibit SARS-CoV-2 virus neutralisation by said anti-S neutralizing antibodies. This reactivity may be tested by standard antigen/antibody binding assays such as ELISA and the like or by standard virus neutralisation assay that are well-known in the art such as those disclosed in the examples of the application. The amino acid positions are indicated according to the numbering in the sequence SEQ ID NO: 2.

The S protein antigen or S antigen according to the present disclosure has at least 90% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2. In some embodiments, the S antigen has 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2.

In some embodiments, said RBD antigen comprises or consists of an amino acid sequence having at least 90% identity with SEQ ID NO: 4. The RBD antigen fragment may have 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity with SEQ ID NO: 4. The RBD antigen fragment according to the present disclosure refers to a functional fragment which is bound by anti-S neutralizing antibodies in standard antigen/antibody binding assays such as ELISA and the like and competitively inhibit SARS-CoV-2 virus neutralisation by said anti-S neutralizing antibodies in standard virus neutralization assays. In some preferred embodiments, said RBD antigen fragment consists of the amino acid sequence SEQ ID NO: 4 or a sequence having at least 90% identity with SEQ ID NO: 4.

In some particular embodiments, the S antigen or RBD antigen fragment thereof comprises one or more mutations within the RBD selected from the group consisting of: K417N or K417T, N439N, L452R, Y453F, S477N, E484K, F490S, and N501Y, said positions being indicated according to the numbering in the sequence SEQ ID NO: 2. The S or RBD antigen may have 1, 2, 3, 4, 5, 6 or all of said mutations. In some particular embodiments, the S or RBD antigen comprises at least one mutation close to the pocket of contact with the receptor ACE2 (region 480-505) chosen from E484K, F490S, and N501Y; preferably at least the E484K and/or N501Y mutations.

In some preferred embodiments, the S or RBD antigen comprises the following mutations: N501Y; E484K and N501Y; K417T or K417N, E484K and N501Y; K417N, N439N, Y453F, S477N, E484K, F490S, and N501Y; K417N, N439N, L452R, S477N, E484K, F490S, and N501Y. In some more preferred embodiment, the S antigen comprises or consists of an amino acid sequence having at least 90% identity with any one of SEQ ID NO: 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64 and 66, wherein said variant comprises one or more of said mutations within the RBD domain. In some more preferred embodiment, the RBD antigen comprises or consists of an amino acid sequence having at least 90% identity with any one of SEQ ID NO: 32, 34, 36 and 38, wherein said variant comprises one or more of said mutations within the RBD domain.

In some particular embodiments, the S antigen comprises a mutation which inactivates the furin cleavage site (PRRAR; positions 681 to 685 in SEQ ID NO: 2). Examples of such furin site mutation, including deletion or substitution are well-known in the art and include the deletion of residues P681 to A684 (Johnson et al., Nature, 2021, doi.org/10.1038/s41586-021-03237-4) and the R682G, R683S and/or R685S substitutions. In some preferred embodiments, the S antigen comprises the R682G, R683S and R685S substitutions. In some more preferred embodiment, the S antigen comprises or consists of an amino acid sequence having at least 90% identity with SEQ ID NO: 30, wherein the variant comprises said furin site mutation.

In some particular embodiments, the S antigen comprises a mutation which stabilizes the Spike trimer. Such mutations which are well-known in the art include the K986P and V987P mutations (S-2P variant) and other proline substitutions, in particular F817P, A892P, A899P and A942P, which can be combined together to obtain a multiple proline variant, in particular hexaproline variant (HexaPro). In some preferred embodiments, the S antigen comprises the K986P and V987P mutations, and eventually one to four additional proline mutations selected from the group consisting of F817P, A892P, A899P and A942P. In some more preferred embodiment, the S antigen comprises or consists of an amino acid sequence having at least 90% identity with any one of SEQ ID NO: 42, 48, 50, 56, 58, 64 and 66, wherein the variant comprises at least one of said Proline mutations.

In some particular embodiments, the S antigen comprises a C-terminal deletion of 1 to 25 or more amino acids, preferably 5 to 25, 10 to 25 amino acids; more preferably 18 to 25 amino acids (18, 19, 20, 21, 22, 23, 24, 25). In some preferred embodiments, the S antigen comprises the deletion of the C-terminal residues from position K1255 (deletion K1255 to T1273). In some more preferred embodiment, the S antigen comprises or consists of an amino acid sequence having at least 90% identity with any one of SEQ ID NO: 40, 46, 50, 54, 58, 62 and 66, wherein the variant comprises said C-terminal deletion.

In some particular embodiments, the S antigen comprises one or more mutations selected from the group consisting of: the substitutions L18F, T20N, P26S, D80A, D138Y, R190S, D215G, A570D, D614G, H655Y, P681H, A701V, T716I, S982A, T1027I, D1118H and V1176F; and the deletions delta 69-70, delta 144 and delta 242-244. In some preferred embodiments, the S antigen comprises at least five of said substitutions outside the RBD, and eventually also at least one or two of said deletions. In some more preferred embodiment, the S antigen comprises or consists of an amino acid sequence having at least 90% identity with any one of SEQ ID NO: 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64 and 66, wherein said variant comprises one or more of said mutations outside the RBD domain.

The percent amino acid or nucleotide sequence identity is defined as the percent of amino acid residues or nucleotides in a Compared Sequence that are identical to the Reference Sequence after aligning the sequences and introducing gaps if necessary, to achieve the maximum sequence identity and not considering any conservative substitution as part of the sequence identity. Sequence identity is calculated over the entire length of the Reference Sequence. Alignment for purposes of determining percent amino acid or nucleotide sequence identity can be achieved in various ways known to a person of skill in the art, for instance using publicly available computer software such as the GCG (Genetics Computer Group, Program Manual for the GCG Package, Version 7, Madison, Wisconsin) pileup program, or any of sequence comparison algorithms such as BLAST (Altschul et al., J. Mol. Biol., 1990, 215, 403-10), FASTA or CLUSTALW.

The nucleic acid construct sequence is codon-optimized for expression in human. Codon optimization is used to improve protein expression level in living organism by increasing translational efficiency of target gene. Appropriate methods and softwares for codon optimization in the desired host are well-known in the art and publically available (see for example the GeneOptimizer software suite in Raab et al., Systems and Synthetic Biology, 2010, 4, (3), 215-225). Codon optimization of the nucleic acid construct sequence relates to the coding sequences but not to the other (non-coding) sequences of the nucleic acid construct.

In some embodiments, the nucleic acid construct comprises a sequence chosen from SEQ ID NO: 1 and SEQ ID NO: 3, the nucleotide sequences having at least 80% identity with said sequences, and the RNA sequences thereof. The nucleotide sequences may have 81%, 82%, 83%, 84%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity with SEQ ID NO: 1 or SEQ ID NO: 3.

In some preferred embodiments, the nucleic acid construct comprises a Kozak consensus sequence or Kozak sequence which is a nucleic acid motif that functions as the protein translation initiation site in most eukaryotic mRNA transcripts. The Kozak sequence may be acc (in position −3 to −1) or cacc (in positions −4 to −1) relative to the atg initiation codon of the S protein antigen or antigen fragment.

In some preferred embodiments, the nucleic acid construct comprises a sequence selected from the group consisting of SEQ ID NO: 10, 12, 14, 16, 18, 20, 22, 24, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, and the nucleotide sequences having at least 80% identity with said sequences, and the RNA equivalent thereof. The nucleotide sequences may have 81%, 82%, 83%, 84%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity with any one of SEQ ID NO: 10, 12, 14, 16, 18, 20, 22, 24, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63 or 65. In some more preferred embodiments, the nucleic acid construct comprises a sequence selected from the group consisting of SEQ ID NO: 14, 16, 18, 20, 22, 24, 31, 33, 35, 37, the nucleotide sequences having at least 80% identity with said sequences, and the RNA sequences thereof. All the above listed sequences are codon-optimized for expression in human and comprise a Kozak sequence. The above listed variants of the listed sequences refer to sequences that are codon-optimized for expression in human and preferably comprising a Kozak sequence.

In some preferred embodiments, said S protein antigen or RBD fragment thereof comprises a signal peptide (SP) or signal sequence. The SP is at the amino terminus of a protein and is involved in transport of the protein to or through cell membranes, transport to different membranous cellular compartments, or secretion of the protein from the cell. Signal peptides are removed from the mature protein during this process by a specific peptidase. For example, the signal peptide may be the natural SP of the S protein (SEQ ID NO: 5) or the SP of a human protein such as CD5 (SEQ ID NO: 6) or IL2 (SEQ ID NO: 7). In some more preferred embodiments, the signal peptide is selected from the group consisting of the sequences SEQ ID NO: 5, 6 and 7 and the derived sequences having a C-ter deletion of 1, 2, 3 or 4 amino acids. In some embodiments, the SP of the human protein further comprises the 1 to 4 amino acid residues in positions +1 to +4 relative to the peptidase cleavage site in said human protein. In some embodiments, the SP of the SARS-CoV-2 S protein antigen (SEQ ID NO: 5) further comprises 1, 2, 3 or 4 amino acid residues at its Cter, preferably comprising V and/or A or is truncated from 1, 2, 3 or 4 amino acid residues at its Cter.

In some preferred embodiments, the S protein antigen or RBD fragment thereof further comprises at least an epitope recognized by human T cells; preferably human CD4+ T-cells; more preferably a Universal Pan HLA-DR Epitope such as PADRE. PADRE is a universal synthetic 13 amino acid peptide (SEQ ID NO: 8) that activates CD4+ T cells. As PADRE binds with high affinity to 15 of the 16 most common human HLA-DR types, it provides potent CD4+ T cell responses, and may overcome problems caused by polymorphism of HLA-DR molecules in human populations. The S protein antigen or fragment thereof and the epitope are advantageously separated by a linker, such as for example preferably a linker comprising or consisting of SEQ ID NO: 9. In some more preferred embodiments, the S protein antigen or fragment thereof comprises PADRE (SEQ ID NO: 8) and preferably further comprises the linker of SEQ ID NO: 9, corresponding to SEQ ID NO: 27. The linker and PADRE sequences are advantageously encoded by the nucleotide sequence SEQ ID NO: 26.

The S antigen and its fragment according to the present disclosure usually do not comprise any other protein moiety or domain other than those disclosed above. In particular, the S antigen and its fragment according to the present disclosure differ from the prior art antigens in that they do not comprise a protein stabilizing moiety such as an immunoglobulin Fc fragment.

In some preferred embodiments, said S protein antigen or RBD fragment thereof comprises an amino acid sequence selected from the group consisting of the sequences SEQ ID NO: 11, 13, 15, 17, 19, 21, 23, 25, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66 and the variant thereof having at least 90% identity (91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity) with one of said sequences. SEQ ID NO: 11, 13, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66 comprise the full length S protein (Spike) sequence including the natural SP. SEQ ID NO: 30 comprises a spike modified at the furin site (spike delta furin). SEQ ID NO: 15, 17, 25, 32, 34, 36 and 38 comprise the RBD with the natural SP at the N-terminus. SEQ ID NO: 19, 21, 23, 25 comprise the RBD with another SP at the N-terminus (SEQ ID NO: 6 or 7). SEQ ID NO: 13, 17, 21 and 25 comprise the linker (SEQ ID NO: 9) and PADRE at the C-terminus (SEQ ID NO: 27).

In some more preferred embodiments, the nucleic acid construct encodes a RBD fragment having a sequence selected from the group consisting of the sequences SEQ ID NO: 15, 17, 19, 21, 23, 25, 32, 34, 36, 38 and the variant thereof having at least 90% identity (91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity) with one of said sequences.

A variant according to the present disclosure refers to a functional variant which is bound by anti-S neutralizing antibodies in standard antigen/antibody binding assays such as ELISA and the like and competitively inhibit SARS-CoV-2 virus neutralisation by said anti-S neutralizing antibodies in standard virus neutralization assays

In some embodiments, said nucleic acid construct is a mammalian expression cassette, preferably human expression cassette, wherein the coding sequence of said S protein antigen or RBD fragment thereof is operably linked to appropriate regulatory sequence(s) for their expression in an individual's target cells or tissue(s). In some particular embodiments, the target cell(s) or tissue(s) is epithelial cell(s) or tissue(s). Such sequences which are well-known in the art include in particular a promoter, and further regulatory sequences capable of further controlling the expression of a transgene, such as without limitation, enhancer, terminator and intron. In some particular embodiments, the expression cassette comprises a promoter; preferably further comprises one or more of an enhancer, terminator or intron.

The promoter may be a tissue-specific, ubiquitous, constitutive or inducible promoter that is functional in the individual's target cells or tissue, in particular epithelial cell(s) or tissue(s). Examples of constitutive promoters which can be used in the present invention include without limitation: phosphoglycerate kinase promoter (PGK), elongation factor-1 alpha (EF-1 alpha) promoter including the short form of said promoter (EFS), viral promoters such as cytomegalovirus (CMV) immediate early enhancer and promoter (optionally with the CMV enhancer), cytomegalovirus enhancer/chicken beta actin (CAG) promoter, SV40 early promoter and retroviral 5′ and 3′ LTR promoters including hybrid LTR promoters. Preferred ubiquitous promoter is CMV promoter. Examples of inducible promoters which can be used in the present invention include Tetracycline-regulated promoters. The promoters are advantageously human promoters, i.e., promoters from human cells or human viruses. Such promoters are well-known in the art and their sequences are available in public sequence data bases.

In some embodiments, the nucleic acid construct encodes other antigen(s), in particular human vaccine antigen(s) from other pathogens.

In some preferred embodiments, the nucleic acid construct is DNA, wherein the coding sequence of said S protein antigen or RBD fragment thereof is operably linked to appropriate regulatory sequence(s) for their expression in an individual's target cells or tissue(s) as disclosed above. The DNA construct advantageously comprises a mammalian expression cassette as disclosed above.

In some other preferred embodiments, the nucleic acid construct is RNA, preferably mRNA, wherein the coding sequence of said S protein antigen or RBD fragment thereof is operably linked to appropriate regulatory sequence(s) for their expression in an individual's target cells or tissue(s). mRNA vaccines are well-known in the art (reviewed in Jackson et al., Vaccines, 2020, 5, 11, doi.10.1038). mRNA is delivered into the host cell cytoplasm where expression generates the antigen of interest. mRNA construct comprises a cap structure, 5′ and 3′untranslated regions (UTRs), and open reading frame (ORF), and a 3′poly(A) tail. mRNA construct may be non-replicating mRNA (MRM) or self-amplifying mRNA (SAM). SAM comprises the inclusion of genetic replication machinery derived from positive-strand mRNA viruses, most commonly alphaviruses such as Sindbis and Semliki-Forest viruses. In SAM constructs, the ORF encoding viral structural protein is replaced by the transcript encoding the vaccine antigen of interest, and the viral RNA-dependent RNA polymerase is retained to direct cytoplasmic amplification of the replicon construct. Trans-replicating RNA are disclosed for example in WO 2017/162461. RNA replicon from alphavirus suitable for gene expression are disclosed in WO 2017/162460. mRNA manufacturing process uses plasmid DNA (pDNA) containing a DNA-dependent RNA polymerase promoter, such as T7, and the corresponding sequence for the mRNA construct. The pDNA is linearized to serve as a template for the DNA-dependent RNA polymerase to transcribe the mRNA, and subsequently degraded by a DNase process step. The addition of the 5′cap and the 3′poly(A) tail can be achieved during the in vitro transcription step or enzymatically after transcription. Enzymatic addition of the cap can be accomplished by using guanylyl transferase and 2′-O-methyltransferase to yield a Cap0^((N7Me)GpppN) or Cap1 (^(N7Me)GpppN^(2′-oMe)) structure, respectively, while the poly-A tail can be achieved through enzymatic addition via poly-A polymerase. mRNA is then purified using standard methods suitable for mRNA purification such as high-pressure liquid chromatography (HPLC) and others. Methods for producing mRNA are disclosed for example in WO 2017/182524.

To improve translation efficiency in vaccinated subject cells, the mRNA construct according to the invention comprises a sequence which is codon-optimized for expression in human. Further improvements of the mRNA construct according to the invention to improve its stability and translation efficiency in vivo include optimization the length and regulatory element sequences of 5′-UTR and 3′UTR; base and/or sugar modifications in the cap structure to increase ribosomal interaction and/or mRNA stability; and modified nucleosides. Modified nucleosides may be in the 5′-UTR, 3′-UTR or ORF. Examples of modified nucleosides include pseudouridine and N-1-methylpseudouridine that remove intracellular signalling triggers for protein kinase R activation. Examples of modified nucleosides that reduce RNA degradation into cells are disclosed in WO 2013/039857. Modified cap structures are disclosed in WO 2011/015347 and WO 2019/175356. Optimized 3′-UTR sequences are disclosed in WO 2017/059902. Modified polyA sequences which improve RNA stability and translation efficiency are disclosed in US 2020/0392518. Modified mRNA with improved stability and translation efficiency are also disclosed in WO 2007/036366.

The invention also relates to a vector comprising the nucleic acid construct according to the present disclosure. The invention may use any vector suitable for the delivery and expression of nucleic acid into individual's cells, in particular suitable for vaccination. Such vectors that are well-known in the art include viral and non-viral vectors.

Non-viral vector includes the various (non-viral) agents which are commonly used to either introduce or maintain nucleic acid into individual's cells. Agents which are used to introduce nucleic acid into individual's cells by various means include in particular polymer-based, particle-based, lipid-based, peptide-based delivery vehicles or combinations thereof, such as with no limitations cationic polymer, dendrimer, micelle, liposome, lipopolyplex, exosome, microparticle and nanoparticle including lipid nanoparticle (LNP) and viral-like particles; and cell penetrating peptides (CPP).

In some embodiments, said nucleic-acid delivery agent comprises tetrafunctional non-ionic amphiphilic block copolymers comprising at least one hydrophilic block and at least one hydrophobic block. Such agents are disclosed in WO 2019/092002.

Agents which are used to maintain nucleic acid into individual's cells include in particular naked nucleic acid vectors such as plasmids, transposons and mini-circles. These vectors have minimal eukaryotic sequences to minimize the possibility of chromosomal integration. Examples of such vectors are the plasmids pVAX1 and pGWIS which are commercially available. In addition, these approaches can advantageously be combined to introduce and maintain the nucleic acid of the invention into individual's cells.

In some embodiments, a plasmid, preferably with minimal eukaryotic sequences, comprising an expression cassette including the nucleic acid construct according to the present disclosure is combined with a nucleic-acid delivery agent, preferably an agent comprising tetrafunctional non-ionic amphiphilic block copolymers comprising at least one hydrophilic block and at least one hydrophobic block as disclosed above.

In some embodiments, a mRNA construct according to the present invention as disclosed above is combined with a nucleic-acid delivery agent suitable for delivery of mRNA into mammalian host cells that are well-known in the art. The mRNA delivery agent may be a polymeric carrier, polycationic protein or peptide, lipid nanoparticle or other. For example, the mRNA (non-replicating or self-amplifying) may be delivered into cells using polymers, in particular cationic polymers, such as polyethylenimine (PEI), poly-L-Lysin (PEL), polyvinylamine (PVA) or polyallylamine (PAA), wherein the mRNA is preferentially present in the form of monomers, dimers, trimers or oligomers as disclosed in WO 2021/001417. Alternatively, the mRNA may be combined with polyalkyleneimine in the form of polyplex particles, suitable for intramuscular administration as disclosed in WO 2019/137999 or WO 2018/011406. The mRNA may also be combined with a polycation, in particular protamine, as disclosed in WO 2016/000792. One or more mRNA molecules may be formulated within a cationic lipid nanoparticle (LNP); for example the formulation may comprise 20-60% cationic lipid; 5-25% non-cationic lipid, 25-55% sterol and 0.5-15% PEG-modified lipid as disclosed WO 2015/164674. The mRNA may also be formulated in RNA decorated particles such as RNA decorated lipid particles, preferably RNA decorated liposomes as disclosed in WO 2015/043613.

Viral vectors are by nature capable of penetrating into cells and delivering nucleic acid(s) of interest into cells, according to a process named as viral transduction. As used herein, the term “viral vector” refers to a non-replicating, non-pathogenic virus engineered for the delivery of genetic material into cells. In viral vectors, viral genes essential for replication and virulence are replaced with an expression cassette for the transgene of interest. Thus, the viral vector genome comprises the transgene expression cassette flanked by the viral sequences required for viral vector production. As used herein, the term “recombinant virus” refers to a virus, in particular a viral vector, produced by standard recombinant DNA technology techniques that are known in the art. As used herein, the term “virus particle” or “viral particle” is intended to mean the extracellular form of a non-pathogenic virus, in particular a viral vector, composed of genetic material made from either DNA or RNA surrounded by a protein coat, called the capsid, and in some cases an envelope derived from portions of host cell membranes and including viral glycoproteins. As used herein, a viral vector refers to a viral vector particle.

A preferred viral vector for delivering the nucleic acid of the invention is a vaccine vector, preferably selected from the group consisting of poxvirus such as vaccinia virus, replication-defective alphavirus replicons, cytomegalovirus, adenovirus, modified vaccinia virus Ankara, vesicular stomatitis virus and measles virus (For a review, see Humphreys et al., Immunology, 2017, 153, 1-9). In some particular embodiment, the viral vector is selected from the group consisting of: cytomegalovirus, adenovirus, modified vaccinia virus Ankara, vesicular stomatitis virus and measles virus.

In particular embodiments, the vector is a particle or vesicle, in particular lipid-based micro- or nano-vesicle or particle such as liposome or lipid nanoparticle (LNP). In more particular embodiments, the nucleic acid is RNA, in particular mRNA and the vector is a particle or vesicle, in particular LNP as described above. The LNP:mRNA mass ratio can be around 10:1 to 30:1.

In some embodiments, vector comprises another nucleic acid construct coding another antigen, in particular human vaccine antigen(s) from other pathogens.

The nucleic acid construct, preferably comprising an expression cassette, is useful for producing recombinant SARS-CoV-2 virus S protein antigen and fragment thereof comprising the receptor-binding domain (RBD) according to the present disclosure by expression from an appropriate recombinant expression vector in a suitable cell system (eukaryotic including mammalian and insect cells or prokaryotic). For example, the vector may be a plasmid in mammalian cells or a baculovirus vector in insect cells.

Therefore, the invention also relates to a host cell (eukaryotic or prokaryotic) modified with a recombinant vector comprising the nucleic acid construct according to the present disclosure.

Immunogenic or Vaccine Composition and Therapeutic Use

The invention further provides an immunogenic or vaccine composition comprising a comprising a nucleic acid construct or vector according to the present disclosure.

The immunogenic or vaccine composition may comprise a mixture of different nucleic acid constructs or vectors according to the present invention. In particular, the composition may comprise a mixture of nucleic acid constructs or vectors encoding variants of the S antigen and/or RBD antigen as described herein. In some embodiments, the composition encodes at least two S and/or RBD antigens having different mutations within the RBD sequence and/or outside the RBD sequence as described herein. In some preferred embodiments, the pharmaceutical composition encodes at least two, three or four different RBD antigens selected from the group consisting of the sequences SEQ ID NO: 15, 32, 34, 36 and 38.

In some embodiments, the pharmaceutical composition further comprises a pharmaceutically acceptable vehicle and/or an adjuvant.

The pharmaceutical vehicles are those appropriate to the planned route of administration, which are well known in the art.

Non-limitative examples of adjuvants suitable for use in the composition of the invention include: CpG oligodeoxynucleotide, polyI:C (polyinosinic-polycytidylic acid), oil emulsion, mineral substances, bacterial extracts, saponin, aluminium salts, monophosphoryl-lipid A (MPL) and squalene.

The pharmaceutical composition comprises a therapeutically effective amount of the nucleic acid construct or vector sufficient to induce an immune response, in particular a protective immune response against SARS-CoV-2 virus infection, in the individual to whom it is administered. The pharmaceutically effective dose depends upon the composition used, the route of administration, the physical characteristics of the specific individual under consideration, concurrent medication, and other factors, that those skilled in the medical arts will recognize.

The pharmaceutical composition of the present invention is generally administered according to known procedures, at dosages and for periods of time effective to induce a beneficial effect in the individual. The administration may be by injection or by mucosal administration, in particular intranasal administration, or mixed administration. For example, the administration may be by intramuscular, intradermal, intravenous or subcutaneous injection, transdermal (such as patch) or intranasal (such as spray) applications, oral, or mixed. In some embodiments, the administration is intramuscular, intranasal or mixed intranasal and intramuscular. The pharmaceutical composition may comprise between 10 ng and 10 mg of nucleic acid construct or vector of the invention; preferably between 100 ng and 2.5 mg, more preferably between 1 μg and 500 μg. The pharmaceutical composition is administered 1 to 3 times at intervals of 2 to 25 weeks. In some embodiments, the pharmaceutical composition is administered according to a prime-boost regimen comprising 2 or 3 administrations in total, preferably intramuscular, intranasal or mixed. In some preferred embodiments the prime-boost regimen comprises 2 administrations at interval of at least 3 weeks, preferably 3, 4, 5 or 6 weeks. In some other preferred embodiments the prime-boost regimen comprises 3 administrations at intervals of up to 3 weeks, preferably 1 or 2 weeks.

In some embodiments, several pharmaceutical compositions, comprising different nucleic acid constructs or vectors according to the present invention are administered separately or sequentially. In particular, several pharmaceutical compositions encoding different variants of the S antigen and/or RBD fragment thereof are administered separately or sequentially. In some embodiments, the pharmaceutical compositions all together encode at least two different RBD antigens selected from the group consisting of the sequences SEQ ID NO: 15, 32, 34, 36 and 38.

In some embodiments of the invention, the immunogenic or vaccine composition induces humoral and cellular immune responses against said SARS-CoV-2 virus; preferably wherein the humoral immune response comprises neutralizing antibodies against said SARS-CoV-2 virus, in particular SARS-CoV-2 and/or the cellular immune response comprises CD4+ and/or CD8+ T-cells against said SARS-CoV-2 virus.

The invention also relates to the immunogenic or vaccine composition according to the present disclosure, for use in the prevention or treatment of SARS-CoV-2 virus infection.

The invention provides also a method for preventing SARS-CoV-2 virus infection in an individual, comprising: administering a therapeutically effective amount of the pharmaceutical composition according to the invention to the individual.

Antigen, Diagnostic and Therapeutic Uses

The invention also relates to the SARS-CoV-2 virus S protein antigen or fragment thereof comprising the receptor binding domain according to the present disclosure.

The SARS-CoV-2 virus Spike (S) protein antigen has at least 90% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO: 2. The S antigen fragment comprises an amino acid sequence having at least 90% identity with SEQ ID NO: 4.

In some preferred embodiments, said S protein antigen or fragment thereof comprises a signal peptide (SP) or signal sequence. The SP is at the amino terminus of a protein and is involved in transport of the protein to or through cell membranes, transport to different membranous cellular compartments, or secretion of the protein from the cell. Signal peptides are removed from the mature protein during this process by a specific peptidase. For example, the signal peptide may be the natural SP of the S protein (SEQ ID NO: 5) or the SP of a human protein such as CD5 (SEQ ID NO: 6) or IL2 (SEQ ID NO: 7). In some more preferred embodiments, the signal peptide is selected from the group consisting of the sequences SEQ ID NO: 5, 6 and 7.

In some preferred embodiments, the S protein antigen or fragment thereof further comprises at least an epitope recognized by human T cells; preferably human CD4+ T-cells; more preferably a Universal Pan HLA-DR Epitope such as PADRE. PADRE is a universal synthetic 13 amino acid peptide (SEQ ID NO: 8) that activates CD4+ T cells. As PADRE binds with high affinity to 15 of the 16 most common human HLA-DR types, it provides potent CD4+ T cell responses, and may overcome problems caused by polymorphism of HLA-DR molecules in human populations. The S protein antigen or fragment thereof and the epitope are advantageously separated by a linker, such as for example preferably a linker comprising or consisting of SEQ ID NO: 9. In some more preferred embodiments, the S protein antigen or fragment thereof comprises PADRE (SEQ ID NO: 8) and preferably further comprises the linker of SEQ ID NO: 9, corresponding to SEQ ID NO: 27.

The S antigen and its fragment according to the present disclosure usually do not comprise any other protein moiety or domain other than those disclosed above. In particular, the S antigen and its fragment according to the present disclosure differ from the prior art antigens in that they do not comprise a protein stabilizing moiety such as an immunoglobulin Fc fragment.

In some preferred embodiments, said S protein antigen or fragment thereof comprises an amino acid sequence selected from the group consisting of the sequences SEQ ID NO: 11, 13, 15, 17, 19, 21, 23, 25, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, and the variant thereof having at least 90% identity (91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity) with one of said sequences. SEQ ID NO: 11, 13, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66 comprise the full length S protein sequence including the natural SP. SEQ ID NO: 30 comprises a spike modified at the furin site (spike delta furin). SEQ ID NO: 15, 17, 25, 32, 34, 36 and 38 comprise the RBD with the natural SP at the N-terminus. SEQ ID NO: 19, 21, 23, 25 comprise the RBD with another SP at the N-terminus (SEQ ID NO: 6 or 7). SEQ ID NO: 13, 17, 21 and 25 comprise the linker (SEQ ID NO: 9) and PADRE at the C-terminus (SEQ ID NO: 27). A variant according to the present disclosure refers to a functional variant which is bound by anti-S neutralizing antibodies in standard antigen/antibody binding assays such as ELISA and the like.

The SARS-CoV-2 virus S protein antigen and fragment thereof comprising the receptor binding domain according to the present disclosure are useful as reagent for the detection or diagnosis of SARS-CoV-2 virus.

In some aspects, the method of detection or diagnosis of SARS-CoV-2 virus comprises determining the presence of antibodies against said virus or thereto in a sample.

The detection or diagnosis is generally performed by immunoassay. Immunoassays are well-known techniques for antibody detection which rely on the detection of antigen-antibody complexes using an appropriate label. The method of the invention may use any immunoassay such as with no limitations, immunoblotting, immunoprecipitation, ELISA, immunocytochemistry or immunohistochemistry, and immunofluorescence like flow cytometry assay, and FACS. The method of the invention may use any appropriate label used in immunoassays such as enzymes, biotin, fluorescent dyes/proteins or others.

In some embodiments, the method of detection or diagnosis of SARS-CoV-2 virus infection comprises the step of:

-   -   incubating the SARS-CoV-2 virus S protein antigen or fragment         thereof comprising the receptor binding domain according to the         present disclosure with the biological sample to form a mixture;         and     -   detecting antigen-antibody complexes in the mixture.

The sample for anti-SARS-CoV-2 virus antibody detection is preferably body fluid from the individual, in particular serum.

The antigen is preferably labeled and the antigen-antibody complexes are detected by measuring the signal from the label by any appropriate means available for that purpose as disclosed above.

In some embodiments, the detecting step comprises the determination of the amount of bound antibody in the mixture, and optionally, comparing the amount of bound antibody in the mixture with at least one predetermined value.

The detection of the antibody in a sample from the individual using the methods of the invention is indicative of whether the individual is suffering from SARS-CoV-2 virus past or present infection.

Therefore, the above methods of the invention are useful for the diagnosis of SARS-CoV-2 virus infection in an individual, in particular the diagnosis of the disease caused by SARS-CoV-2 virus, ranging from febrile illness to severe acute respiratory syndrome.

In some embodiments, the above methods comprise the step of deducing therefrom whether the individual is suffering from SARS-CoV-2 virus infection i and in particular from a disease caused by SARS-CoV-2 virus.

In some embodiments in connection with this aspect of the invention, the above methods comprise a further step of administering an appropriate treatment to the individual depending on whether or not the individual is diagnosed with SARS-CoV-2 virus virus infection and in particular with a disease caused by SARS-CoV-2 virus.

Another aspect of the invention is a kit for the diagnosis or detection of SARS-CoV-2 virus, comprising at least one antigen for the detection of SARS-CoV-2 virus antibody, as defined above, preferably further including a detectable label.

Another aspect of the invention, relates to an immunogenic or vaccine pharmaceutical composition comprising, as active substance a SARS-CoV-2 virus S protein antigen or a fragment thereof comprising the receptor binding domain according to the present disclosure, in association with at least one pharmaceutically acceptable vehicle.

The pharmaceutical vehicles are those appropriate to the planned route of administration, which are well known in the art.

The pharmaceutical composition may further comprise a carrier and/or adjuvant. Non-limitative examples of carriers suitable for use in the composition of the invention include uni- or multi-lamellar liposomes, ISCOMS, virosomes, viral pseudo-particles, saponin micelles, saccharid (poly(lactide-co-glycolide)) or gold microspheres, and nanoparticles. Non-limitative examples of adjuvants suitable for use in the composition of the invention include: CpG oligodeoxynucleotide, polyI:C (polyinosinic-polycytidylic acid), oil emulsion, mineral substances, bacterial extracts, saponin, aluminium salts, monophosphoryl-lipid A and squalene.

The pharmaceutical composition comprises a therapeutically effective amount of the antigen sufficient to induce a protective immune response against SARS-CoV-2 virus infection in the individual to whom it is administered. The pharmaceutically effective dose depends upon the composition used, the route of administration, the physical characteristics of the specific human under consideration, concurrent medication, and other factors, that those skilled in the medical arts will recognize.

The invention provides also a SARS-CoV-2 virus S protein antigen or a fragment thereof comprising the receptor binding domain according to the present disclosure for use as a medicament.

The invention provides also a SARS-CoV-2 virus S protein antigen or a fragment thereof comprising the receptor binding domain according to the present disclosure or pharmaceutical composition according to the invention for use in the prevention or treatment of SARS-CoV-2 virus infection and associated disease.

The invention provides also a method for preventing or treating SARS-CoV-2 virus infection and associated disease, comprising: administering a therapeutically effective amount of the pharmaceutical composition according to the invention to the individual.

The pharmaceutical composition of the present invention is generally administered according to known procedures, at dosages and for periods of time effective to induce a beneficial effect in the individual. The administration may be by injection or mucosal administration, in particular respiratory such as intranasal administration.

The practice of the present invention will employ, unless otherwise indicated, conventional techniques which are within the skill of the art. Such techniques are explained fully in the literature.

The invention will now be exemplified with the following examples, which are not limitative, with reference to the attached drawings in which:

FIGURE LEGENDS

FIG. 1 . Phylogenetic analysis of representative Betacoronaviruses and SARS-CoV-2 based on full length genome sequences.

The tree is midpoint rooted for ease of visualization, and high bootstrap values are indicated at key nodes.

FIG. 2A-B. Homology modelling of the S protein of SARS-CoV-2 using the Swiss-Model tool (FIG. 2A) and showing the model based on the top-hit (PDB ID: 6ACD) (FIG. 4C B).

The putative RBD is highlighted with a black box in the alignment. The QMEAN score reflects the modelling quality. Similar results were obtained using Phyre2.

FIG. 3 . Schematic representation of the selected antigens.

SP: Signal Peptide. RBD: Receptor Binding Domain.

FIG. 4A-C. SARS-CoV-2 neutralizing antibody titers in immunized BALB/c mice.

FIG. 4A Immunization scheme. Groups of 5 female Balb/c mice were immunized intra muscularly with 100 μg of pVAX vector containing the sequence of either the SARS-CoV-2 spike (pVAX-Spike), the spike with a mutated furin cleavage site (pVAX-Spike-deltaFurin), the receptor binding domain with the signal peptide of the spike (pVAX-RBD), the same RBD antigen with the PADRE sequence in 3′ (pVAX-RBD-PADRE), or an empty vector (pVAX).

FIG. 4B Neutralizing antibody titers against SARS-CoV-2 at day 27 post immunization (prime), determined by plaque reduction neutralizing test (PRNT₅₀).

FIG. 4C Neutralizing antibody titers against SARS-CoV-2 at day 47 post immunization (prime-boost), determined by PRNT₅₀.

FIG. 5A-D. Immunogenicity and protective efficacy.

Groups of 5-8 female Balb/c mice were immunized intra muscularly (i.m.) with 100 μg of pVAX vector containing the sequence of the spike receptor binding domain with the signal peptide of the spike (pVAX-RBD) or an empty vector (pVAX). The immunization route was either i.m., intra nasal (i.n.) or a mix of i.m. for prime then i.n. for boosts, at 7-10 days intervals. At day 42 post initial immunization, mice were challenged i.n. with 1.10⁵ PFU of a mouse adapted SARS-CoV-2 strain. Viral load in the lungs was assessed at day 3 post infection.

FIG. 5A Immunization and challenge scheme.

FIG. 5B Neutralizing antibody titers against SARS-CoV-2 at day 42 post immunization (prime-boost-boost), determined by plaque reduction neutralizing test (PRNT₅₀).

FIG. 5C Viral load (genomes copies as PFU equivalents) measured in the lungs at day 3 post challenge.

FIG. 5D Viral load (PFU per g of tissue) measure in the lungs at day 3 post challenge.

FIG. 6 . ratio of IgG2a/IgG1 or Th1/Th2 responses.

The content of sera of Balb/c mice immunized with the receptor binding domain with the signal peptide of the spike (pVAX-RBD) using an i.m. prime-boost protocol were assessed by isotype specific ELISA against the SARS-CoV-2 RBD.

EXAMPLES Material and Methods

1. Design of the Antigens

Phylogenetic analysis of publicly available SARS-CoV-2 (2019-nCov) full-length sequences (NCBI sequence data base) with representative sequences for the genus Betacoronavirus indicates that SARS-CoV-2 is part of a well-defined Sarbecovirus clade that includes viruses sampled in bats (FIG. 1 ).

It is significantly different from the well-known human sarbecovirus SARS-Cov with only 79% identity at the nucleotide level over the full length of the genome. This value drops to 72.7% for S in nucleotides, and 76.2% in amino acids. However structural modelling using the Swiss-Model program (Waterhouse et al., Nucleic Acids Res., 2018 Jul. 2; 46(W1): W296-W303) or Phyre2 (Kelley et al., Nat Protoc. 2015 June; 10(6):845-58) and a representative sequence of the S protein of 2019-nCov (SARS-CoV-2) as query suggest a similar structural organization to the S protein of SARS-Cov, with core sections showing stronger sequence or structure conservation and modeling quality, and variation (with modelling uncertainty) mostly in the surface residues (FIG. 2 ).

In particular, a putative RBD of SARS-CoV-2 can be defined with, like for SARS-Cov (SARS-CoV-1), a core and an external subdomain. As it has been shown for other coronaviruses (Embemovirus MHV, HCov-229E or SARS-Cov), the RDB is highly reactive to anti-S neutralizing antibodies, and could comprise the key epitopes of the neutralizing response.

Based on the state of the art of betacoronaviruses biology, and in particular building on the structural similarity with SARS-Cov, the S protein is the most relevant antigen to include regardless of the delivery strategy. Two antigens have thus been designed (FIG. 3 ). One corresponds to the complete S protein, and the second, smaller (minimal) antigen, for ease of expression and production, correspond to the SARS-CoV-2 RBD of the S protein. To ensure secretion of the RBD antigen, 3 signal peptides (SP) have been selected.

Specifically, antigen 1 consists of 1273 amino acids or 3822 nucleotides, and the sequence has been codon-optimized for expression in Homo sapiens. Antigen 2 consists of 194 amino acids or 582 nucleotides, and the sequence has been codon-optimized for expression in Homo sapiens. Antigen 2 is combined with one of 3 SP (from the SARS-CoV-2) S protein; from the human CD5 or from the human IL-2). Other versions of Antigen 2 having SP variants according to the present disclosure are also engineered, one with a SP lacking SA in positions 20-21 of SEQ ID NO: 23; one with a SP lacking RLVA in positions 25 to 28 of SEQ ID NO: 19; and one with a SP lacking A in positions 20 of SEQ ID NO: 15.

These antigens can be delivered as nucleic acid immunogens, formulated with appropriate non-viral agent such as amphiphilic block copolymer or in a viral vector.

The antigens were also combined with a universal Pan HLA-DR Epitope termed PADRE. PADRE is a universal synthetic 13 amino acid peptide that activates CD4+ T cells. As PADRE binds with high affinity to 15 of the 16 most common human HLA-DR types, it provides potent CD4+ T cell responses and may overcome problems caused by polymorphism of HLA-DR molecules in human populations.

2. Plasmid Construction

The various cDNA sequences designed from 2019-nCov (SARS-CoV-2 or SARS2) sequences were codon-optimized for Homo sapiens expression, synthesized (Thermo-Fisher Scientific), and cloned into the pVAX-1 plasmid (Thermo-Fisher) under the control of a CMV promoter and containing a Kozak sequence. The cDNA sequences correspond to SEQ ID NO: 10, 12, 14, 16, 18, 20, 22, 24, 29, 31, 33, 35 in the attached sequence listing and encode r a protein antigen corresponding to the amino acid sequences SEQ ID NO: 11, 13, 15, 17, 19, 23, 25, 30, 32, 34 and 36, respectively in the attached sequence listing. pVAX-Spike comprises the cDNA of SEQ ID NO: 10 encoding a Spike of SEQ ID NO: 11. VAX-Spike-deltaFurin comprises the cDNA of SEQ ID NO: 29 encoding a Spike-deltaFurin of SEQ ID NO: 30. pVAX-RBD comprises the cDNA of SEQ ID NO: 14 encoding a RBD of SEQ ID NO: 15. pVAX-RBD-PADRE comprises the cDNA of SEQ ID NO: 16 encoding a RBD-PADRE of SEQ ID NO: 17. All pVAX derived plasmids were amplified in Escherichia coli and plasmid DNA was purified on EndoFree plasmid purification columns using the NucleoBond Xtra Maxi EF Kit (Macherey Nagel). The constructs were verified by enzymatic digestion and by SANGER sequencing.

3. Formulation

The SARS-2 DNA vaccine is formulated by mixing equal volumes of ABC stock solution (Nanotaxi®, provided by In-Cell-Art; disclosed on page 13 to 17 of WO 2019/092002) in water and plasmid DNA solution at the desired concentration in 2× buffer solution, immediately prior to intramuscular injection. The mixing of ABC Nanotaxi® and plasmid DNA is a self-assembly process that results from hydrogen bonding, hydrophobic, and electrostatic interactions between ABC and DNA.

4. Antigen Expression/Western Blot Analysis

293 cells are transfected with plasmids expressing the antigens. After 24 h, cell lysates and supernatant are harvested. Samples are fractionated by SDS-PAGE and transferred to cellulose membranes to be probed with anti-S antibodies or sera. A goat anti-mouse immunoglobulin G (IgG)-horseradish peroxidase (HRP) conjugate is used as secondary antibody. Peroxidase activity is visualized with an enhanced chemiluminescence detection kit (Thermo Fisher Scientific).

5. Animal Vaccination

Animal experiments are performed according to institutional, French and European ethical guidelines (Directive EEC 86/609/ and Decree 87-848 of 19 Oct. 1987) subsequent to approval by the Institut Pasteur Safety, Animal Care and Use Committee, protocol agreement delivered by the local ethical committee and the Ministry of High Education and Research. Groups of at least 5 female Balb/c, transgenic K18-ACE2 (McCray et al., J. Virol., 2007, 81(2), 813-821), or other mice type, including C57BL/6C mice and interferon deficient mice such as IFNAR mice were housed under specific pathogen-free conditions in individually ventilated cages during the immunization period at the Institut Pasteur animal facilities. Mice were vaccinated with different constructs using a prime/boost regimen. Formulations was injected bilaterally into both tibial anterior muscles using an 8-mm, 30-gauge syringe (intra muscular (i.m.)), or intra-nasally (i.n.) at different time intervals. Mice were anesthetized by isoflurane before injection. A group of five unvaccinated mice, housed alongside the treated mice was used as controls. Sera were collected at various time points post-immunization to monitor the immune responses.

6. Cell Culture

Vero C10008 clone E6 (CRL-1586, ATCC) cells were maintained in Dulbecco's modified Eagle medium (DMEM) complemented with 10% heat-inactivated serum, 100 U/mL penicillin and 100 μg/mL streptomycin and were incubated at 37° C. and 5% CO2.

7. ELISA

Measurement of anti-S IgG antibody titers in serum of vaccinated mice is performed using either a commercial kit or an in house assay. Recombinant SARS-CoV-2 RBD were coated on 96-well MAXISORP plates. Coated plates were incubated overnight at 4° C. The plates were washed 3 times with PBS-0.05% Tween, then blocked 1 h at 37° C. with PBS-0.05% Tween-3% BSA. Serum samples from immunized mice were serially diluted and incubated for 1 h at 37° C. on the plates. HRP-conjugated isotype-specific (IgG1 or IgG2a) secondary antibodies were used to reveal the specific and relative amounts of IgG isotypes. Endpoint titers for each individual serum were calculated as the reciprocal of the last dilution giving twice the absorbance of the negative control sera.

8. Plaque Reduction Neutralization Test (PRNT)

For plaque reduction neutralization titer (PRNT) assays, Vero-E6 cells are seeded onto a 24-well plate and incubated at 37° C. for 12-24 h to 90% confluency. Two-fold serial dilutions of heat-inactivated serum samples are mixed with 50 PFU of SARS-CoV-2 for 1 h at 37 C, then added to cells for 2 h at 37° C. Virus/serum mix are then aspirated, and cells washed with PBS and overlaid with 1 mL of DMEM supplemented with with 5% fetal calf serum and and 1.5% carboxymethylcellulose. The plates were incubated for 3 days at 37° C. with 5% CO2. Viruses were then inactivated and cells fixed and stained with a 30% crystal violet solution containing 20% ethanol and 10% formaldehyde. Serum titer was measured as the dilution that reduced SARS-CoV-2 plaques by 50% (PRNT₅₀). This test was performed on several SARS-CoV-2 lineages as seen in the circulation in human. The SARS-CoV-2 lineages included in particular clade L, clade G (GISAID) and lineages B.1.1.7 (UK variant), B.1.351 (South Africa variant) and P.1 (Brazil variant).

9. SARS-CoV-2 Challenge

Animals were transferred to an isolator in BioSafety Level 3 animal facilities of Institut Pasteur. Mice were anesthetized by intra peritoneal (i.p.) injection of a mixture of Ketamine and Xylazine, transferred into a biosafety cabinet 3 where they were inoculated i.n. with either 1.10⁵ PFU of a mouse adapted strain of SARS-CoV-2 (MaCo3) for wild type Balb/C mice or 1.10⁴ PFU of a low passage clinical isolate (BetaCoV/France/GES-1973/2020) for the transgenic K18-ACE2 mice. The isolate BetaCoV/France/GES-1973/2020 was supplied by the National Reference Centre for Respiratory Viruses hosted at Institut Pasteur (Paris, France) and headed by Pr. Sylvie van der Werf.

Three days after challenge, mice were sacrificed and lung samples were collected aseptically, weighted, and mechanically homogenized in ice-cold PBS. The presence of SARS-CoV-2 in the lung was detected by titration on VeroE6 cells and by detecting viral RNA using a RT-qPCR (nCoV_IP4) targeting the RdRp gene, as described on the WHO website (https://www.who.int/docs/default-34source/coronaviruse/real-time-rt-pcr-assays-for-the-detection-of-sars-cov-2-institut-35pasteur-paris.pdf?sfvrsn=3662fcb6_2).

As SARS-CoV-2 infection is lethal for K18-ACE2 mice, symptoms and weights were monitored for 14 days after challenge.

10. Lung Histopathology

Samples from the lung were fixed in formalin for at least 7 days and embedded in paraffin for histopathological examination.

Results

A prime-boost protocol with 4 weeks intervals between immunizations was first used to evaluate the immunogenicity of the different constructs. 100 μg of the pVAX plasmid containing either the complete SARS-CoV-2 spike, a spike modified at the furin site (spike delta furin), only the receptor binding domain (RBD) with the native signal peptide of the spike or the RBD with the PADRE sequence in 3′ (RBD-PADRE) was injected intra-muscularly (i.m.) The plasmid DNA was mixed with an amphiphilic bloc copolymer for delivery.

The neutralizing potential of the sera was evaluated at day 27 (prior to the second immunization), and 20 days later (FIG. 4A). The neutralization plaque reduction neutralizing tests (PRNT₅₀) on the different constructs revealed that the smallest antigen (RBD) with the native signal peptide of the spike and without the PADRE sequence resulted in an early response already detectable 4 weeks after the prime (FIG. 4B), and which was more homogenously and consistently boosted by the second immunization in comparison to the other constructs (FIG. 4C).

Using the RBD construct, an accelerated protocol of a prime with two boosts, administered at 7-10 days intervals was next used (FIG. 5A). At day 42, the neutralizing potential of sera elicited using i.m, intra nasal (i.n.) and a mix of i.m. prime followed by boosts using the i.n. route was compared.

However, the challenge with a mouse adapted strain of SARS-CoV-2 inoculated i.n. revealed that the mixed protocol of i.m. and i.n. resulted in a lower viral load in the lungs of the animals in terms of viral RNA copies (FIG. 5C) and no infectious particles could be detected by titration. As expected from the PRNT results, mice immunized only by the i.n. route presented viral loads comparable to the mock vaccinated (empty vector pVAX) group (FIG. 5D). This shows that an accelerated immunization scheme over a short period of time can lead to strong neutralizing antibody titers.

As IgG isotype switching can serve as indirect indicators of Th1 and Th2 responses, the SARS-CoV-2 RBD-specific IgG1 and IgG2a isotype titers were determined in the sera of Balc/c mice immunized with the RBD antigen. Significantly higher IgG2a antibody titers than IgG1 were observed, reflecting a predominant Th1-type immune response (FIG. 6 ).

In conclusion, this study indicates that the RBD antigen is able to provide protection from a SARS-CoV-2 challenge of immunized animals, correlating with strong neutralizing antibody induction. 

1. An immunogenic composition comprising an mRNA construct encoding a SARS-CoV-2 virus Spike (S) protein antigen comprising a signal peptide comprising the amino acid sequence of SEQ ID NO:5, wherein said mRNA construct has a cDNA sequence having at least 90% identity with the nucleotide sequence of SEQ ID NO:10, and wherein said mRNA construct has a cDNA sequence comprising a Kozak sequence comprising the sequence CACC in positions −4 to −1 relative to the AUG initiation codon of the S protein antigen, and a lipid nanoparticle for introducing the mRNA into cells.
 2. The immunogenic composition of claim 1, wherein the S protein comprises an amino acid sequence having at least 90% identity with SEQ ID NO:
 4. 3. The immunogenic composition of claim 1, wherein the S protein antigen has at least 95% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO:2.
 4. The immunogenic composition of claim 1, wherein the S protein antigen has at least 97% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO:2.
 5. The immunogenic composition of claim 1, wherein the S protein antigen has at least 99% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO:2.
 6. The immunogenic composition of claim 1, wherein the S protein antigen has 100% identity with the amino acid sequence from positions 19 to 1273 of SEQ ID NO:2.
 7. (canceled)
 8. (canceled)
 9. The immunogenic composition of claim 1, wherein said Kozak sequence comprises the sequence GCCACC in positions −6 to −1 relative to the ATG initiation codon of the S protein antigen.
 10. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence comprising an RBD sequence consisting of nucleotides 1-582 of SEQ ID NO:3.
 11. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 91% identity with the nucleotide sequence of SEQ ID NO:10.
 12. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 93% identity with the nucleotide sequence of SEQ ID NO:10.
 13. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 95% identity with the nucleotide sequence of SEQ ID NO:10.
 14. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 97% identity with the nucleotide sequence of SEQ ID NO:10.
 15. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 98% identity with the nucleotide sequence of SEQ ID NO:10.
 16. The immunogenic composition of claim 1, wherein said mRNA construct has a cDNA sequence having at least 99% identity with the nucleotide sequence of SEQ ID NO:10.
 17. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 91% identity with the nucleotide sequence of SEQ ID NO:10.
 18. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 93% identity with the nucleotide sequence of SEQ ID NO:10.
 19. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 95% identity with the nucleotide sequence of SEQ ID NO:10.
 20. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 97% identity with the nucleotide sequence of SEQ ID NO:10.
 21. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 98% identity with the nucleotide sequence of SEQ ID NO:10.
 22. The immunogenic composition of claim 9, wherein said mRNA construct has a cDNA sequence having at least 99% identity with the nucleotide sequence of SEQ ID NO:10. 